Tension control for web printing machines



June 30, 1959 A, sc m-r 2,892,597

TENSION CONTROL FOR WEB PRINTING MACHINES I Filed April 4, 1957 2 Sheets-Sheet '1 FIG. I.

E INVENTOR m ATTORNEYJ June 30, 1959 F. A. SCHMIDT 2,892,597

TENSION CONTROL FOR WEB PRINTING MACHINES Filed April 4, 1957 2 Sheets-Sheet 2 FIG. 2.

I ATTORNEYS INVENTORY W4 W BY United States Patent '0 ce Patented June 30, 1959 TENSION CONTROL FOR WEB PRINTING MACHINES Fred A. Schmidt, Louisville, Ky.

Application April 4, 1957, Serial No. 650,783

6 Claims. (Cl. 242-7542) This invention relates to tension controls for web printing machines.

In web printing machines, the paper is supplied from a roll of paper and the tension is regulated by applying varying driving or braking forces to the'r'oll, either through its core or its periphery, and under the control of a tension sensing device, such as a pilot roller. The roll is usually carried in a reel or other device which may also carry one or more other unused rolls and which is equipped with devices for transferring the web feed from an expiring roll to a new roll without reducing the speed of travel of the web. Suitable tension control is also required during the operations involved in such a roll change or paster,'as well as during the stopping of the machine.

Fully automatic tension controls now in extensive use are generally of two types. In one such control, a running roll is controlled by peripherally acting belts which also serve to bring a new roll up to running web speed, the tension being controlled by varying the contact pressure or angle of wrap of these belts with the roll. In the other system, the control of the active web supplying roll is by means of straps whose pressure against the roll may be regulated, and the speeding up of a fresh or replacement roll is accomplished through a drive acting on the core of the roll instead of its periphery.

In the system of the present invention, the same belts are preferably used for accelerating a new roll and for tensioning the web after the splice is made, and these belts may also back up the running Web to give adhesion pressure when the periphery of the new roll is brought into contact with the web running from the expiring roll. The tension is controlled by varying the speed of the belts, as opposed to its wrap or pressure against the roll, providing a highly advantageous type of control and facilitating the use of the same belts for both tensioning purposes and for the acceleration of a replacement roll.

- The control itself uses an error signal made up of signal'components proportional to web speed, tension belt drive speed and deviation of tension from desired value. Compensation for reel rotation in making a splice is achieved by introducing into this error signal a fourth component, proportional to the speed of reel rotation, and the desired stopping tension is similarly obtained by variation in the proportionality factor applicable to the tension deviation component of the error signal. An inherently stable system is obtained, in which the correction is exponential and rapid and in which there is practically no tendency for hunting to occur. The feeding back into the error signal of the tension belt drive speed, or a component proportional to the control signal which varies this speed, permits obtaining a true proportional control without loss of sensitivity or hunting due to the rather considerable inertia of the paper roll. Difliculties due to variation in diameter or moment of inertia of the roll as the paper is unwound are substantially eliminated.

In the preferred system according to the present in}, vention, mechanical adjustments are reduced to a minimum, and the control system may comprise essentially a circuit, havingvariable elements such as tachometers and variable resistors, for introducingthevarious signal corn-- ponents, together with switch elements, for altering the relevant circuit constants, to take into account alteredi conditions such as the rotation of the reel in either direction, the stopping of the press, andso on. The system has marked advantages in thatth e necessary adjustments may practically all take place in the circuit itself, as dis; tinguished from the controlling or controlled mechanical elements and that the circuit elements may be readily protected from dirt, paper dust, ink or other factors which might tend to alter or interfere with operation.

A tension system embodying the invention. in a pre Fig. 1 is a schematic showing a reel changer embodying the invention in a preferred form;

Fig. 2 is a circuit diagram showing the control system of the invention. I I The control system of the present invention may be,

applied to any of a variety of reels or web roll supporting devices containing means for supporting web rolls and giving them the required movements involved in affecting; a roll change along with means for holding them in posi-j tion for cooperation with tension control and web splicing mechanisms. i 4

Fig. 1 shows schematically one suitable arrangement, of elements. As there indicated, a three arm reel 11 is supported on a pedestal 2, and has means for rotatablyj supporting a running roll R1, replacement roll ,R-2 and expired roll or sub R-3. The web W is led around a guide and back up roller 3, floating roller 4 and further guide roller 5 and passestherefrom to theprinting ma-, chine, which may be of anytype, such as intaglio, relief or planographic, and may be either monotone or multicolor. The details of construction of a reel of the character shown are well known and will not be referred to in the present application except where necessary for a" full understanding of the present invention. Reference may be made to prior patents for such details as are not. referred to in the present application. Driven belt B is associated with the running roll R-l for controlling the tension of the web and also serves to bring a replacement roll up to speed, as later described. This belt is carried around fixed guide pulleys 6 positioned so as to give a; suitable angle of wrap on the roll R-1 and is maintained under predetermined tension by a movable pulley'7, the pressure of which against the belt B is maintained at a suitable constant value by means of an air piston 8. The belt is thus enabled to follow the roll as it diminishes inv diameter due to consumption of the paper thereon and also to contact the roll in various positions whilemaintaining a fixed belt tension. Pully 9 drives the beltin a manner described below. The sequence of movements. of the reel is well known in itself and willbe reviewed. briefly at this point to the extentnecessary for an understanding of the present invention.

As the web W is fed, the tension is measured by the floating roller 4 and the speed of the drive pulley9 is regulated accordingly, so as to maintain constant tension on the web W. As the web roll R-l approaches exhaustion, the reel is rotated to bring this roll into the position occupied by expired roll R-3, or somewhat beyond this position and to bring the replacement roll against the back up roller 3 (or, rather, against the e N r 2,892,597 r expiring web which is passing around this roll) and the making of a splice and severing of theexpired web are then accomplished in the known manner. As the expiring roll passes out of the control of belts B, B, it is temporarily tensioned by means of brake mechanism 32 acting on its core, and the replacement roll which has simultaneously been brought underthe control of belts B, is brought up to speed thereby, preliminary to the making of the splice. The present invention is not concerned with specific mechanism by which or manner in which the foregoing movements are accomplished, but with the tensioning and roll accelerating control system now about to be described.

The essential control throughout is by variation of the speed of belts B, B, which speed variation is accomplishedthrough drive motor 11, coupled to the driven pulley 9 through a belt 12 which may be of the so-called Gilmer timing belt type, and also coupled through a similar belt 13 to a tachometer generator 51 of familiar type, which consists essentially of a direct current genorator producing a voltage proportional to the rotational speed.

The motor 11 is supplied with driving current through a controller indicated schematically at 14, which supplies a motor drive voltage through output 15 which is proportional to an input signal applied across input connection 16. Any of various suitable electronic or mechanical controllers 14 may be utilized, an amplidyne generator, in particular, has been found suitable. Means for controlling the motor 11 through amplidyne 14 is provided and comprises a master tachometer 50, which again takes the form of a direct current generator driven at a speed proportional to the web speed, as by means of roller 17 bearing against the web as it passes over guide roller 5. As will be apparent, this tachometer may be driven by the web or by any of various cylinders in the printing machine so long as speed of rotation is proportional to web speed. The voltage produced by tachometer 50 enters into the error signal utilized by controlling tension belt speed in a manner described below.

, The floating roller 4 measures the tension in the web W. This roller may be mounted in any convenient way. In particular, it may be carried on arms 20 pivoted at 21 and provided with counterweights 22 for regulating the speed of response, if desired. Regulated pressure may be applied to the floating roller as by means of an air cylinder 23 connected to an air line 24. A potentiometer 52 may be coupled to the arm 20 as by means of a cable and spring arrangement 25, 26 operating against a drum 27 which moves the contact arm of the potentiometer proportionally to the movement of the floating roller. The pressure in cylinder 23 being normally constant, it will be apparent that the floating or pilot roller 4 would remain stationary if the tension in the web is of a corresponding value but will move (to the right in Fig. 1) if the web tension slackens below this value and will move in the opposite direction (to the left in Fig. 1) if the web tension increases. The corresponding movement of potentiometer 52 is utilized to produce a voltage which is combined with the voltages of the tachometers 50 and 51 for producing an error signal for controlling the tension belts B.

Other elements entering into the control system in various phases of its operation include a reel drive motor M, which through worm 30 and worm wheel 31 rotates the reel either forwardly or reversely, as desired, and the core brakes 32 which may be of magnetic type and operate otf a commutator 33 concentric with the reel shaft but held stationary as by means of a weight 34. The essential elements of the control system are shown in Fig. 2, and comprise a master tachometer 50 which produces a voltage proportional to the web speed, reel tachometer 51, which produces a voltage proportional to the speed of the reel drive motor, and potentiometer .4 52, the position and setting of which varies in accordance with the tension as sensed or measured by the floating roller, together with appropriate circuit elements as described below for producing an error signal of suitable type.

The first component of the error signal is a voltage proportional to the deviation of the tension from set value, and this component is produced in the following manner: The winding 53 of potentiometer 52, previously referred to, is connected through resistors 54 and 55 across lines L-l and L-2, which are maintained at fixed voltage ditference with respect to each other, a voltage across lines L-1 and L-2 of 105 volts D.C. being suitable. This voltage may be supplied from any suitable floated or ungrounded source, and in particular may be provided by voltage supply comprising transformer 56, rectifier 57, filter circuit 58 and voltage regulator tube 59, as indicated. The moving contact 68 of potentiometer 52 will accordingly be at a potential depending upon its position on potentiometer winding 53, as determined by the floating roller position. This potential is balanced as later described against the potential of the contact 61 of potentiometer 61, 62, the winding 62 of which is connected through fixed resistors 63 and 64 and potentiometer winding 66 and 68 across the lines L-1, L2, previously referred to.

For purposes later indicated, contact arm 67 of potentiometer 66, 67 is connected through a switch 70 to line L-l, and the contact arm 69 of potentiometer 68, 69 is connected through a switch 71 to line L2. Also, a further connection from potentiometer winding 62 through aresistor 72 of potentiometer 73, 74 and switch 75 to the line L-l is provided. For present purposes, it is sufficient to note that by setting the contact arm 61, the balanced potential of contact arm 60 is established, which permits adjustment through contact arm 61 of the desired zero or neutral setting of the tension. Connections 76 and 77 from the contact arms 60 and 61 lead, rfirst, to a low pass filter, consisting of adjustable resistor 78 and condenser 79, which circuit absorbs relatively high frequency transient voltage variations, preventing the introduction of such components into the error signal. The higher frequency components are applied through resistor 80 across the winding 81 of potentiometer 81, 82. The value of the output signal may be regulated by suitably setting contact arm 82 and this signal is developed across connections 77 and 83. Switches 84 and 85, normally in the positions indicated, are provided for purposes described later.

As will be apparent, there is developed across connections 77 and 83 a voltage proportional to the voltage difference between contacts 60 and 61 and, hence, proportional to the deviation of tension from set value, which voltage may be regulated by means of the setting of contact arm 82 so as to apply an appropriate proportionality factor to this component in the error signal. As previously noted, higher frequency variations may be eliminated by means of the filter circuit 78, 79 and the time constant of this circuit may be adjusted by the setting of variable resistor 78, as desired.

The reel tachometer 51 is connected to ground line 86 and is shunted by winding 87 of potentiometer 87, 88 and fixed resistor 89, as indicated. Contact 88 is connected through connection 90 and connection 83, and line 77, previously referred to, forms one output 91 of the control signal, which thus includes a component developed across potentiometer winding 87 and proportional to the reel motor speed and a component developed across potentiometer winding 81 which is proportional to the tension error signal.

The master tachometer 50 is similarly connected to ground line 86 and shunted by the winding 92 of potentiometer 92, 93 and fixed resistor 94. The second output line 95 is connected to contact arm 93. With reference to ground line 86, it will be apparent that a signal is developed across outputs 91, 95 consisting of a voltage proportional to reel motor speed augmented or diminished by the tension error signal component (output line 91) balanced against a voltage proportional to web speed (output line 95).

As will be apparent, if the tension is at set value, the voltages with reference to ground of outputs 91, 95 will be equal so that zero output signal is developed. Any disturbance of conditions such as a change in web speed or achange in web tension will create an unbalance in the outputs 91, 95 and produce an error signal which is applied to amplidyne 96 which controls the reel motor speed, hence producing an appropriate adjustment of reel motor speed and restoring the balanced condition.

The balanced condition, apart from transient factors, can exist only where the tension is that of the set value. If it be supposed that the voltages in output connections 91, 95 are balanced by reason of the positive tension error signal component plus the negative reel tachometer signal component (tension too heavy and reel motor running too slow), it will be apparent that an unstable condition has been created, in which, by reason of the difference between web speed and reel motor speed, the tension error signal component will increase further, creating an output signal resulting in the speeding up of the reel motor. While the secondary effect of this speeding up to reduce tension and, hence, reduce tension error signal component, the primary or immediate effect is to increase the reeltachometer error signal component, thus increasing the error signal as a whole and tending to restore conditions to a true balance more rapidly. In accordance with familiar principles applicable to control systems, it will be clear that the system is inherently balanced and requires at all times the return of potentiometer contacts 60 to proper balanced position, so that tension may be controlled even from narrow limits.

It will be noted that by setting potentiometer contacts 82, 88 and 93, an output error signal which is a linear combination of components proportional to tension deviation, reel motor speed and web speed, is produced, and that the proportionality factors or constants applied to these components in this linear function may be varied as desired. In particular, by setting contact 82, the sensitivity to tension deviation may be regulated by comparison with the follow up signal fed back to the reel tachometer, this regulation being of importance primarily for the elimination of hunting and production of a rapid exponential return to set conditions following any disturbance. Secondly, the setting of contact 93 as compared with contact 88, or vice versa, permits first of all the balancing of tachometers where the voltages produced by them may for one reason or another not be proportional to the relative speeds with the same proportionality constants. Thirdly, the setting of these contacts permits the adjustment of the system so that the peripheral speed of the belts or other roll driving elements may in a balanced condition, with zero error signal, be slightly less than the web speed, and in accordance with the slippage of belts on the roll.

As will be apparent, the system of the invention has great flexibility and simplicity in operation. For example, it is not necessary to determine the exact amount of slip which may occur, as this factor may be taken into account by the setting of contact arm 88 and the optimum condition may be determined very simply by cut and try determination of the position of this arm which provides the most suitable operation.

As the reel is rotated, the peripheral web roller velocity component is increased or diminished by a velocity component due to the reel rotation on its own axis, which reel rotation velocity component might upset the operation of the system as thus far described. Accordingly, the switch 70 previously referred to, is provided, this switch closing when the reel is rotated in a forward direction and shorting out through contact 67 part of the potentiometer 68 and again canceling out the effect of the reel rotation. When the press is stopped, switch 75,-,

closes, connecting resistor 72 of potentiometer 73, 74

across resistors 63, 66, again unbalancing the voltage of contact 61 so that the neutral setting is disturbed and the system will operate to maintain a desired higher stop-.

ping tension, as opposed to the usual running tension, the

effect of this adjustment being the same as a shift of.

the position of contact arm 61.

Closing switch and opening switch 84 cuts out the" tension error signal, which may be done for balancing the speeds as indicated by tachometers 50, 51 andalso for cutting out the tension error signal component during.

the paster. As will be apparent, when the paster is to, be made the tension error signal is taken from the expiring web while the belts 8 are running against the replacement roll, so that elimination of this signal component is desirable at that time.

What is claimed is: I 1. In a web tension control for printing machines, tension belts for engaging and driving a web roll, variable speed means for driving said belts and control means. for said variable speed means, the said control means comprising a follow-up tachometer producing a signal component proportional to the belt speed, a master tachometer producing a signal component proportional to the running web speed, tension responsive means producing a signal component proportional to the tension in the running web, means for combining the three said signal components to produce an error signal which is a substantially linear function of the three said component signals, and means for varying the speed of the said variable speed means proportionally to the said error signal.

In a web tension control for printing machines, tension belts for engaging and driving a web roll, variable speed means for driving said belts and control means for said variable speed means, the said control means comprising a follow-up tachometer producing a signal component proportional to the belt speed, a master tachometer producing a signal component proportional to the running web speed, tension responsive means producing a signal component proportional to the tension in the running web, means for combining the three said signal components to produce an error signal which is a substantially linear function of the three said component signals, and comprising adjustable means for varying the proportionality constants applied to the said components in the said function, and means for varying the speed of the said variable speed means proportionally to the said error signal.

3. In a web tension control for printing machines, tension belts for engaging and driving a web roll, variable speed means for driving said belts and control means for said variable speed means, the said control means comprising a follow-up tachometer producing a signal component proportional to the belt speed, a master tachometer producing a signal component proportional to the running web speed, tension responsive means producing a signal component proportional to the tension in the running web and including a low pass filter for eliminating higher frequency elements of the said signal component, means for combining the three said signal com ponents to produce an error signal which is a substantially linear function of the three said component signals, and means for varying the speed of the said variable speed means proportionally to the said error signal.

4. In a web tension control for printing machines, tension belts for engaging and driving a web roll, vari.

able speed means fordriving said belts and control means fors'aid, variablevspe'ed means, the said control means prising a followup tachometer producing a signal i'on'ent proportional to the belt speed, a master tacl io eter producing a signal component proportional to the running web speed, tension responsive means prodiicing asignal component proportional to the difference in tension in the running web from a predetermined tension value, means for combining the three said signal components to produce an error signal which is a substantially linear function of the three said component signals, m eans' for varying the speed of the said variable speed means proportionally to the said error signal, ajs'top switch, and means co'ntrolled by said stop switch for shifting the said predeten'nined tension value to a second and higher predetermined tension value.

5'. In a web tension control for printing machines, tension be'lts for engaging and driving a web roll, variable speed means for driving said belts and control means for said variable speed means, the said control means comprising a follow-up tachometer producing a signal component proportional to the belt speed, a master tachometer producing a signal component proportional to the running web speed, tension responsive means producing a signal component proportional to the tension in the running web, a reel rotation switch and means controlled thereby for producing also a signal component representing roll peripheral velocity due to reel rotation, means for combining the said signal components to pro duce an error signal which is a substantially linear function of the three said component signals, and means for varying the speed of the said variable speed means proportionally to the said error signal.

6. In a web tension control for printing machines, tension belts for engaging and driving a web roll, variable speed means for driving said belts and control means for said variable speed means, the said control means comprising a follow-up tachometer producing a signal component proportional to the belt speed, a master tachometer producing a signal component proportional to the running web speed, tension responsive means producing a signal component proportional to the tension in the running web, means for combining the three said signal components to produce an error signal which is a substantially linear function of the three said component signals, means for vaiying the speed of the said variable speed means proportionally to the said error signal, roll core brake means for controlling web tension during a splice, and switch means for cutting out the signal component proportional to tension during the p aster.

References Cited in the file of this patent UNITED STATES PATENTS 2,361,856 McMullen et al. Oct. 31, 1944 2,617,610 Bennett et al. Nov. 11, 1952 FOREIGN PATENTS I 480,541 Great Britain Feb. 24, 1938 

